Joint replacement surgery involves replacing an existing joint with artificial prosthetic components. Examples of common joint replacements include hip replacements and knee replacements. Hip replacement may be segmented into three types: primary, revision and resurfacing. Primary hip replacement, also called Total Hip Arthroplasty (THA), involves the surgical excision of the head and proximal neck of the femur and removal of the acetabular cartilage and subchondral bone. Commonly, an artificial canal is created in the proximal medullary region of the femur, and a metal femoral prosthesis is inserted into the femoral medullary canal. An acetabular component or implant is then inserted proximally in the enlarged acetabular space.
Hip resurfacing, like THA, involves the surgical removal of the acetabular cartilage and subchondral bone, and the subsequent insertion of an acetabular prosthetic. Unlike THA, resurfacing does not involve the excision of the femoral head, but rather covering the existing femoral head with a prosthetic cap, which mates with the acetabular prosthetic. Hip resurfacing is often done with younger patients to preserve femoral bone stock for future revisions.
Revision hip surgery is typically performed when an artificial hip joint fails, due to factors such as infection, loosening, fracture, mechanical failure or instability. Revision hip surgery typically involves the replacement of one or more of the failed artificial prosthetics, depending on the reasons for failure.
Nearly 1,000,000 hips are replaced in North America and Europe every year. Approximately 75% of these procedures are primary, with 15% revision and 10% resurfacing. Studies indicate that the number of hip replacements will increase over the coming years due to many factors.
An important aspect of hip replacement is ensuring proper alignment of the acetabular component or implant with respect to the pelvis. Specifically, studies have shown that failure to properly align the acetabular component or implant with the pelvis may lead to premature wear, propensity to dislocate and patient discomfort.
Another important aspect of hip replacement is ensuring the change in leg length and offset resulting from the procedure is acceptable. Typically, the goal is to leave the leg length and offset unchanged as a result of the procedure. However, surgeons will often incorporate a small change in leg length as a corrective measure.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, similar reference numerals may be used among the figures to indicate corresponding or analogous elements (e.g. reference sensor 811 of FIG. 8 is analogous to reference sensor 1211 of FIG. 12).